The interview coincided with the release of his upcoming memoir Big Blue Sky on Wednesday.

In one passage of the book, read by interviewer Melissa Doyle, Mr Garrett claimed the safety of Australia was potentially threatened while Mr Rudd was leader.

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Kevin Rudd Peter Garrett in Parliament.Credit:Andrew Meares

"It's a big call, but I stand by it," Mr Garrett said, adding the former Labor prime minister treated people with "an enormous amount of contempt" and made "the business of the country almost ungovernable".

When pushed on what danger he feared Mr Rudd posed, Mr Garrett said the former PM was "unpredictable" and he didn't know what he "could or would do".

"I mean, even with [John] Howard you know where he stood," he said.

"I'm not a great fan of John Howard's, and he wouldn't be a great fan of mine, but that aspect of his prime ministership I sort of understand and respond to."

"If Mr Garrett were serious about these accusations he would have made them five years ago. Not try to rewrite history now."

In his time as environment minister, Mr Garrett was not a member of the cabinet's National Security Committee, which formulates strategies to deal with Australia's security and focuses on other classified matters, and would not have been privy to its decisions.

Peter Garrett is trying to sell a book. I have no idea what else he's doing these days

In another passage from the book, Mr Garrett wrote that supporting Mr Rudd was "certainly the biggest" mistake he made in his political career.

"I've been particularly strong in this book about leadership and Rudd's leadership and I think it needed to be said," Mr Garrett said.

"I'm critical of him, that's true, very critical, but I think for good reason."

Mr Garrett stepped down from politics in 2013, when Julia Gillard was ousted as prime minister.